1. Field of the Invention
The present invention relates to a machine tool and, in particular, to a machine tool that generates an optimum acceleration/deceleration in controlling each axis.
2. Description of the Related Art
In conventional machining of a component, a mold, or the like, a machining program is generated and a machine tool is controlled based on the generated machining program to perform the machining. A machining speed for performing machining is commanded as a movement speed of an axis in a machining program, which is a maximum speed of the relative movement (tool movement) between a tool and a machining object. However, actually, movement data in which a movement speed of each axis is varied according to an acceleration/deceleration time constant of each axis is output to a machine tool at the time of starting machining, or in a corner part, a curve part, or the like. Further, although a machining object has an allowable error and a target machining time, an operator of a machine tool adjusts, while confirming the machining surface quality of the machining object, the allowable error and the target machining time by changing an acceleration/deceleration time constant or changing a speed commanded in a program. Note that in the specification, machining accuracy indicating an error in the shape of an actual machining object with respect to a command position, i.e., the degree to which the shape of the machining object changes smoothly (a scratch or a streak is inconspicuous) is called machining surface quality.
As a related art associated with the adjustment of parameters such as an acceleration/deceleration time constant and a speed in such machining, Japanese Patent Application Laid-open No. 2003-058218 discloses a parameters adjustment method in which a plurality of types of parameters adjustable in machining is prepared and used as a parameter set. Further, Japanese Patent Application Laid-open No. 2006-043836 discloses a machining conditions setting method in which the generation of machining path information and the setting of machining conditions for reducing a machining time in consideration of machining accuracy are performed using a machining pattern.
In general, an increase in machining surface quality at a corner part or a curve part may be realized in such a way that an acceleration/deceleration for controlling a tool in performing machining is entirely decreased, but an entire machining speed is decreased. On the other hand, an acceleration/deceleration may be set to be entirely large to increase a machining speed. However, when a tool is rapidly decelerated and accelerated at a corner part or near a curve part under such a setting, there is a likelihood that vibration occurs in a machine to degrade machining surface quality (a machining surface is scratched).
FIGS. 8A and 8B are diagrams each showing an example in which an acceleration/deceleration suddenly occurs at a corner part of a tool path commanded by a machining program.
When a speed of a tool suddenly changes in various machining such as lathe-turning shown in FIG. 8A and boring machining shown in FIG. 8B, vibration occurs in a machine due to the impact of the change, which causes the degradation of machining surface quality at a corner part or a curve part. When adjusting an acceleration/deceleration while balancing an improvement in machining surface quality and reduction in a machining time in consideration of each element associated with the movement of an axis so as to prevent such phenomena, an operator has to expend much effort and may still not be able to optimize a speed or an acceleration.
As a response to such problems, the prior art techniques disclosed in Japanese Patent Application Laid-open No. 2003-058218 and Japanese Patent Application Laid-open No. 2006-043836 can only deal with situations adapted to a prepared parameter set or a machining pattern, and cannot flexibly deal with a diversity of situations.